DC/DC converters are in widespread use today. A typical application example is the coupling of a DC power source to a rechargeable battery for charging the same via the DC/DC converter with a desired voltage.
A previous approach DC/DC converter is shown in FIG. 1. Therein, a pair of first side terminals 10 is coupled to a first side converter circuit 20, which in turn is coupled to a transformer circuit 30, which in turn is coupled to a second side converter circuit 240, which in turn is coupled to a pair of second side DC terminals 60. Via the transformer circuit 30, galvanic isolation between the pair of first side DC terminals 10 and the pair of second side terminals 60 is achieved.
Both of the first side converter circuit 20 and the second side converter circuit 240 comprise an H bridge circuit. Each H bridge circuit comprises four switching elements. Each switching element is depicted to have a switch and a reverse directed diode in parallel. The switching elements of the second side converter circuit are MOSFETs, which comprise a parasitic diode anti-parallel to the switchable channel from source to drain. Accordingly, the parallel circuit of switch and diode is a possible circuit symbol representation of a MOSFET component.
In a case where power is transferred from the pair of first side DC terminals 10 to the pair of second side DC terminals 60, power is transferred in two different power transfer states. As the power flow is from the pair of first side DC terminals 10 to the pair of second side DC terminals 60, this power transfer direction is also referred to as a forward power transfer, with the two power transfer states being also referred to as forward power transfer states. In a first power transfer state, switches 22 and 28 are closed, and a current flow through the two MOSFET transistors respectively consisting of switch 248 and diode 249 and switch 242 and diode 243 in the second side converter circuit 240 is established. In a second power transfer state, switches 24 and 26 are closed, and a current flow through the two MOSFET transistors respectively consisting of switch 244 and diode 245 and switch 246 and diode 247 in the second side converter circuit 240 is established. The DC/DC converter 2 is controlled to alternate between these two power transfer states, transferring power through the transformer circuit 30 in a galvanically isolated manner.
The switching between the two power transfer states results in voltage peaks in the second side converter circuit 240. These voltage peaks are unacceptable in magnitude, because they are potentially dangerous to the semiconductor elements of the second side converter circuit 240. Therefore, previous approach DC/DC converters are prone to failure arising from damage to the semiconductor components. Alternatively, a control of the DC/DC converter shuts down the same in case of such voltage peaks, giving rise to unacceptable down times of the DC/DC converter as a whole.